For the conventional ink jet head, there is a problem in that ink to be discharged to a printing medium has an occasion of leaking through a joint portion for the members constituting the ink supply passages from the ink container through the discharging outlets, wherein such leaked ink sometimes results in providing a stain onto a print product obtained. In addition, there is also a problem in that when an air bubble should present in the ink pathway, such air bubble is liable to cause a reduction in the energy dedicated for discharging ink, wherein the reduction will make it unable to conduct normal ink discharging. In view of this, in order to prevent the occurrence of such ink leakage and also in order to prevent such air bubble from entering into the ink pathway, there is a proposal in that a sealing material is disposed in the ink jet head or the joint portion of the constituent members for the ink supply passages of the ink jet head.
An example of a known ink jet head provided with such sealing member and an example of a known ink jet apparatus provided with such ink jet head are schematically shown in FIGS. 1 to 4.
FIG. 1 is a schematic slant view illustrating an example of the known ink jet head. FIG. 2 is a schematic cross-sectional view illustrating a cross section of a principal portion, namely a A-B cross-sectional portion, taken along the ink pathway of the ink jet head shown in FIG. 1 and which was viewed in a direction indicated by arrow marks in FIG. 1.
FIG. 3 is a schematic explanatory view of a discharging element portion of the ink jet head shown in FIG. 1. FIG. 4 is a schematic view illustrating an example of an ink jet apparatus provided with the ink jet head shown in FIG. 1.
In FIG. 1, reference numeral 1 indicates an ink jet head. To the ink jet head 1, there is connected an ink supply unit 2 for supplying ink. The ink supply unit 2 is connected to an ink tank 5 through ink supply tubes 3. The ink tank 5 comprises an ink container 5B containing black ink therein and a three-chambered ink container 5C containing yellow ink, magenta ink and cyan ink which are arranged respectively on an opposite side of an aluminum base plate 4 for the ink jet head. Each of these ink containers is provided with an insertion hole into which the ink supply tube 3 can be inserted so that the ink containers can be detachably connected to the ink supply unit 2.
The ink jet head 1 has such constitutions as shown in FIG. 2 and FIG. 3, wherein the ink jet head comprises an electrothermal converting body comprising a heat generating element 103 and wirings 102 for said heat generating element formed by means of the conventional thin film-forming technique on a silicon wafer base member 101. On the silicon wafer base member having said electrothermal converting body formed thereon, there is disposed an ink pathway wall 104 having ink pathway-forming walls 104a and a common ink chamber-forming wall 104b formed by a resin such as a photosensitive resin. Reference numeral 105 indicates a top plate made of glass which is joined so as to cover recesses formed by the ink pathway wall 104 thereby establishing ink pathways and a common ink chamber. The top plate 105 is provided with an opening as a common ink supply port 107. The common ink supply port 107 is covered by a filter 106 for ink. The top plate 105 is provided with a sealing member 110 formed by means of a dispenser or by the screen printing process. The ink supply unit 2 is connected to the common ink supply port through the sealing member 110.
FIG. 4 is a schematic explanatory view of an example of an ink jet apparatus (IJA) provided with an ink jet head cartridge (IJC) comprising the ink jet head shown in FIG. 1.
In FIG. 4, reference numeral 20 indicates an ink jet head cartridge (IJC) provided with a plurality of ink discharging outlets opposite the recording face of a printing sheet transported on a platen 24. Reference numeral 16 indicates a carriage HC for holding the IJC 20 thereon. The carriage is connected to part of a driving belt 18 which serves to transmit a driving force from a driving motor 17, and it is designed such that it can be moved while sliding on a pair of guide shafts 19A and 19B being arranged in parallel with each other. By this, the IJC 20 is made capable of moving back and forth along the entire width of the printing sheet.
Reference numeral 26 indicates a recovery device which is disposed at a predetermined position within the range in which the IJC 20 is moved, specifically, for example, at a position opposite the home position. The recovery device performs capping to the discharging outlets of the IJC 20 by a driving force through a driving mechanism 23 from a motor 22. Further, the discharging outlets of the IJC can be protected by way of capping by means of the recovery device when the printing is terminated.
Reference numeral 30 indicates a blade made of silicone rubber serving as a wiping member which is disposed at a side of the recovery device 26. The blade 30 is held at a blade holding member 30A in the form of a cantilever, and it is operated, as well as in the case of the recovery device 26, by means of the motor 22 and the driving mechanism 23 so as to encounter the outlet face of the IJC. By this, the blade 30 is projected in the range in which the IJC 20 is moved on appropriate timing during the printing operation by the IJC 20 or after recovery treatment by using the recovery device, whereby dew drops, moisture, dusts or the like adhered on the outlet face of the IJC 20 can be swabbed.
As above described, the sealing member is disposed at a position of the ink jet head which is contacted with ink. Because of this, when a coating composition for the formation of the sealing member is applied in an excessive amount, there is an occasion for the sealing member formed to be partly invaded into the ink pathways, wherein such invasion into the ink pathways entails a problem in that some of the discharging outlets are clogged in the worst case. In order that the amount of the coating composition for the formation of the sealing member can be precisely controlled so that the sealing material is not invaded into the ink pathways, there is usually used a coating composition in the liquid state at room temperature.
Particularly, there is used a solvent-free coating material in the liquid state at room temperature. The reason why the formation of the sealing member is conducted using such solvent-free coating material is due to the following points. That is, since the sealing member is disposed such that it unavoidably contacts with ink, when the sealing member contains a solvent, the solvent is liable to elute into the ink thereby modifying the chemical composition of the ink, wherein there will be sometimes occurred a problem in that the ink is not efficiently discharged as desired. Further, the sealing member is disposed at a portion where the constituent members of the ink supply passages are joined, and because of this, the formation of the sealing member is necessary to be conducted while having a due care so that any negative influence is provided for the precision of an ink jet head assembled. Hence, it is desired for the sealing member to be formed by using a one-component coating material having a long working life and which is substantially free from a necessity of having a due care about its working life. Other than these, from the viewpoints in terms of the functional requirements for an ink jet head, the sealing member is required to be sufficient in air tightness and fluid tightness as above described and in addition, it is also required to be low in stress and high in resistance to ink.
Particularly, for instance, in the case of an ink jet head in which the ink passage wall as a constituent thereof is constituted by a material having a large thermal expansion coefficient, the sealing member situated in the vicinity of the discharging element is liable to suffer from a stress caused by a thermal expansion of said material, wherein the sealing member will be sometimes removed. In order to prevent occurrence of the removal problem, it is known that the sealing member is designed to possess an elasticity capable of absorbing such stress. This elasticity effectively works also against an impact which the ink jet head will have upon conducting recovery treatment and the like, specifically, for example, upon conducting wiping treatment.
Further, since the position where the sealing member is disposed is to be directly contacted with ink as above described, the sealing member is required that it is highly resistant against the ink, namely, hardly deteriorated in terms of the function with the ink, and it does not provide an eluate of imparting a negative influence to the ink.
Thus, it is understood that the sealing member disposed in an ink jet head is required to totally satisfy the above described requirements therefor and to exhibit sufficient sealing properties.
In the above described viewpoints, it is known to use a silicone rubber sealant as the sealing member for an ink jet head.
Now, in the case where an air bubble accidentally enters into the common ink chamber or ink passage of an ink jet head, the ink jet head is subjected to recovery treatment using a recovery mechanism including, for example, a suction pump capable of being operated by means of a timer disposed at the apparatus body and in a manually operating manner. In this case, when the air bubble stays on the upper stream side to the energy generating body in the direction for ink to be supplied, in order to remove the air bubble, the recovery treatment is necessary to be conducted by virtue of a remarkable suction force.
By the way, in order to comply with an increased demand for miniaturization of an ink jet apparatus in recent years, there is a tendency for the ink container therefor to be small in terms of the capacity accordingly. This tendency is more apparent as for a cartridge type ink jet apparatus in which an ink container is mounted on a carriage. In the case where the ink container is thus made to be small in terms of the capacity, it is desired to use ink only for the purpose of conducting printing but not for other purposes, wherein the foregoing recovery treatment is desired to be conducted as little as possible.
As the cause for such air bubble to enter into the ink jet head, there are considered a case wherein an air bubble is contaminated during the production of an ink jet head and other case wherein air contained in ink in a dissolved state is released to provide an air bubble due to a temperature rise upon ink discharging. The problem relating to contamination of such air bubble during the use of an ink jet head may be eliminated by subjecting the ink jet head to recovery treatment before its shipment.
However, in the case where the ink jet head having been subjected to recovery treatment is maintained in a non-use state over a long period of time, there will be an occasion when an air bubble is generated within the ink jet head. The generation of such air bubble is usually caused chiefly due to the invasion of air through a sealing member used for sealing the joining portion of constituents for the ink supply passage. Particularly, the conventional silicone rubber sealant by which the sealing member is constituted is high in gas permeability and it is not problematic as long as the ink jet head is used in the ordinary manner, but when the ink jet head is maintained in a non-use state over a long period of time, a problem is liable to entail in that ink vaporizes little by little through the opening as the common ink supply port, wherein air invades through the joint portion in an airtight state by means of the silicone rubber sealant between the common ink supply port and the ink supply unit so as to supplement a pressure difference caused by the vaporization of the ink whereby generating an air bubble. In this case, it is necessary to conduct the foregoing recovery treatment.
In order to eliminate this disadvantage, it is considered to constitute the sealing member by an epoxy resin having an excellent gas barrier property. However, the epoxy resin is insufficient in flexibility in relation to the foregoing stress and because of this, a removal is liable to sometimes occur at the sealing member. Hence, the epoxy resin is not suitable to be used as the sealing member for an ink jet head.
Other than the above, it is considered to constitute the sealing member by an elastic epoxy resin obtained by modifying the epoxy resin so as to have an improved flexibility. However, although such elastic epoxy resin has a satisfactory gas barrier property and a satisfactory flexibility, it is poor in resistance to ink. Thus, the elastic epoxy resin is also not suitable to be used as the sealing member for an ink jet head.
In recent years, an ink jet apparatus has been using not only in the field of printers but also in other fields of copying apparatus and dyeing apparatus. Particularly, ink has been often depositing on OHP sheets, clothes and the like which are different from printing sheets such as papers, using an ink jet apparatus. And print products applied with an improved water proof has been often produced. In this case, highly alkaline ink is usually used in order to attain an improved fixing property and an improved water proof for the print products. Particularly, in order to obtain a print product with an improved fixing property and an improved water proof, ink comprising a dye having a relatively low solubility to a solvent and a pigment having a relatively low dispersibility is sometimes used. Said ink is usually made to be highly alkaline, wherein said dye is desirably solubilized and said pigment is desirably dispersed so that said dye and said pigment can be efficiently utilized.
Along with the use of such highly alkaline ink, there is a demand for attaining an improved ink resistance for the sealing member. In fact, when a conventional ink jet head with the use of highly alkaline ink having been used is allowed to stand without using over a long period of time, there is a tendency that the quantity of air bubbles contaminated into the ink passage is greater than that in the ordinary case and a removal is occurred at the sealing member of the ink jet head having been operated with the use of the highly alkaline ink. Further, in this case, if the ink jet head is of the type that the sealing member is disposed in the vicinity of electric wirings, there is a tendency that a short circuit is occurred between the electrodes.